1. Field of the Invention
The present invention relates to an agent for preventing growth of weeds in rice fields. More particularly, the present invention relates to an agent for preventing growth of weeds in rice fields which is added to water in rice fields to prevent growth of weeds on the surface of soil covered with water in the rice fields by decreasing the amount of light which passes through water covering the soil, does not cause any problem of food sanitation, maintains the effect for a long period of time with stability by repeated applications, is inexpensive and can be used advantageously.
2. Description of the Related Arts
Prevention of growth of weeds in rice fields means control of growth of weeds which compete with rice and maintenance of advantageous conditions in rice fields. Growing rice has been a battle against weeds since ancient times. Huge amounts of labor have been used to remove weeds from rice fields while rice fields used by the human kind have continued to expand. Recently, herbicides which can maintain growth of plants of the rice family and selectively remove weeds in rice fields have been developed and widely used. Although these herbicides satisfy the requirements that they be decomposed in the natural environment, not be accumulated in animals and plants and show no chronic toxicity to human bodies, application of some herbicides is voluntarily discontinued.
Due to the tendency of consumers to prefer natural products and to emphasize sanitation, rice is increasingly required to be grown without using agricultural chemicals. Thus, development of methods of removing weeds in rice fields without using herbicides has been attempted. For example, growth of weeds can be prevented by raising ducks, Triopus longicaudatus or carps in rice fields. Suppressing growth of weeds by intentionally growing algae has been also attempted. It is also attempted that a China ink is added to rice fields to suppress the growth of weeds by the effect of shielding the rice field from light and rice is grown without using agricultural chemicals. However, raising animals has a drawback in that it requires a large amount of labor for the management. Growing algae has drawbacks in that it occasionally causes adverse effects on rice and that algae do not always dominate weeds in the competition. Carbon black which is the raw material of China inks is not free from problems of food sanitation because it is produced from petroleum, natural gas or acetylene although it is kept under the regulation on the food sanitation which requires that benzopyrene be not detected.
Therefore, an agent for preventing growth of weeds in rice fields which causes no problem at all with respect to the food sanitation, exhibits excellent effect of preventing growth of weeds in rice fields, is inexpensive and can be used economically has been desired.